// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef CONTENT_BROWSER_MEDIA_AUDIO_STREAM_MONITOR_H_
#define CONTENT_BROWSER_MEDIA_AUDIO_STREAM_MONITOR_H_

#include <map>
#include <utility>

#include "base/callback_forward.h"
#include "base/macros.h"
#include "base/threading/thread_checker.h"
#include "base/time/default_tick_clock.h"
#include "base/time/time.h"
#include "base/timer/timer.h"
#include "build/build_config.h"
#include "content/common/content_export.h"
#include "media/audio/audio_output_controller.h"

namespace base {
class TickClock;
}

namespace content {

class WebContents;

// Repeatedly polls audio streams for their power levels, and "debounces" the
// information into a simple, binary "was recently audible" result for the audio
// indicators in the tab UI.  The debouncing logic is to: 1) Turn on immediately
// when sound is audible; and 2) Hold on for X amount of time after sound has
// gone silent, then turn off.  Said another way, we don't want tab indicators
// to turn on/off repeatedly and annoy the user.  AudioStreamMonitor sends UI
// update notifications only when needed, but may be queried at any time.
//
// When power level monitoring is not available, audibility is approximated
// with having active audio streams.
//
// Each WebContentsImpl owns an AudioStreamMonitor.
class CONTENT_EXPORT AudioStreamMonitor {
public:
    explicit AudioStreamMonitor(WebContents* contents);
    ~AudioStreamMonitor();

    // Returns true if audio has recently been audible from the tab.  This is
    // usually called whenever the tab data model is refreshed; but there are
    // other use cases as well (e.g., the OOM killer uses this to de-prioritize
    // the killing of tabs making sounds).
    bool WasRecentlyAudible() const;

    // Returns true if the audio is currently audible from the given WebContents.
    // The difference from WasRecentlyAudible() is that this method will return
    // false as soon as the WebContents stop producing sound.
    bool IsCurrentlyAudible() const;

    // Starts or stops audio level monitoring respectively for the stream owned by
    // the specified renderer.  Safe to call from any thread.
    //
    // The callback returns the current power level (in dBFS units) and the clip
    // status (true if any part of the audio signal has clipped since the last
    // callback run).  |stream_id| must be unique within a |render_process_id|.
    typedef base::Callback<std::pair<float, bool>()> ReadPowerAndClipCallback;
    static void StartMonitoringStream(
        int render_process_id,
        int render_frame_id,
        int stream_id,
        const ReadPowerAndClipCallback& read_power_callback);
    static void StopMonitoringStream(int render_process_id,
        int render_frame_id,
        int stream_id);

    void set_was_recently_audible_for_testing(bool value)
    {
        was_recently_audible_ = value;
    }

private:
    friend class AudioStreamMonitorTest;

    enum {
        // Desired polling frequency.  Note: If this is set too low, short-duration
        // "blip" sounds won't be detected.  http://crbug.com/339133#c4
        kPowerMeasurementsPerSecond = 15,

        // Amount of time to hold a tab indicator on after its last blurt.
        kHoldOnMilliseconds = 2000
    };

    // Indicates if monitoring of audio stream power level is available.
    // It's only available if AudioOutputController can and will monitor
    // output power levels.
    static bool power_level_monitoring_available()
    {
        return media::AudioOutputController::will_monitor_audio_levels();
    }

    // Helper methods for starting and stopping monitoring which lookup the
    // identified renderer and forward calls to the correct AudioStreamMonitor.
    static void StartMonitoringHelper(
        int render_process_id,
        int render_frame_id,
        int stream_id,
        const ReadPowerAndClipCallback& read_power_callback);
    static void StopMonitoringHelper(int render_process_id,
        int render_frame_id,
        int stream_id);

    // Starts polling the stream for audio stream power levels using |callback|.
    void StartMonitoringStreamOnUIThread(
        int render_process_id,
        int stream_id,
        const ReadPowerAndClipCallback& callback);

    // Stops polling the stream, discarding the internal copy of the |callback|
    // provided in the call to StartMonitoringStream().
    void StopMonitoringStreamOnUIThread(int render_process_id, int stream_id);

    // Called by |poll_timer_| to sample the power levels from each of the streams
    // playing in the tab.
    void Poll();

    // Compares last known indicator state with what it should be, and triggers UI
    // updates through |web_contents_| if needed.  When the indicator is turned
    // on, |off_timer_| is started to re-invoke this method in the future.
    void MaybeToggle();

    // Helper functions to track number of active streams when power level
    // monitoring is not available.
    void OnStreamAdded();
    void OnStreamRemoved();

    // The WebContents instance to receive indicator toggle notifications.  This
    // pointer should be valid for the lifetime of AudioStreamMonitor.
    WebContents* const web_contents_;

    // Note: |clock_| is always |&default_tick_clock_|, except during unit
    // testing.
    base::DefaultTickClock default_tick_clock_;
    base::TickClock* const clock_;

    // Confirms single-threaded access in debug builds.
    base::ThreadChecker thread_checker_;

    // The callbacks to read power levels for each stream.  Only playing (i.e.,
    // not paused) streams will have an entry in this map.
    typedef std::pair<int, int> StreamID;
    typedef std::map<StreamID, ReadPowerAndClipCallback> StreamPollCallbackMap;
    StreamPollCallbackMap poll_callbacks_;

    // Records the last time at which sound was audible from any stream.
    base::TimeTicks last_blurt_time_;

    // Set to true if the last call to MaybeToggle() determined the indicator
    // should be turned on.
    bool was_recently_audible_;

    // Whether the WebContents is currently audible.
    bool is_audible_;

    // Calls Poll() at regular intervals while |poll_callbacks_| is non-empty.
    base::RepeatingTimer poll_timer_;

    // Started only when an indicator is toggled on, to turn it off again in the
    // future.
    base::OneShotTimer off_timer_;

    // Number of active streams to be used as a proxy for audibility when power
    // level monitoring is not available.
    size_t active_streams_;

    DISALLOW_COPY_AND_ASSIGN(AudioStreamMonitor);
};

} // namespace content

#endif // CONTENT_BROWSER_MEDIA_AUDIO_STREAM_MONITOR_H_
